The nature of the manufacturing process of charge coupled devices (CCDs) has limited the length of such devices to 2,048 pixel sites. Applications requiring the use of longer CCDs have typically employed two or more such CCDs which are staggered or arranged with some overlap. An inherent problem in the use of staggered, overlapping CCDs is the inaccuracy and unreliability of one or more (typically two to four) pixel sites at the junction of the overlapping CCDs. This causes a loss of information and/or a streaking of optical images.
Recently a technique has been developed to butt-join two or more CCDs on a hybrid substrate in order to accommodate applications requiring CCD arrays in excess of 2,048 pixel sites. See "10,240 Pixel Focal Plane With Five Butted 2,048.times.96 Element TDI CCDs", by W. C. Bradley and A. A. Ibrahim, from Proceedings of the Society of Photo-Optical Instrumentation Engineers, Vol. 175, "Airborne Reconnaissance IV", Apr. 17-18, 1979, pp. 72-80. This procedure enables the construction of linear CCD arrays of unlimited length. The butting procedure allows for a more uniform arrangement of two or more CCDs but suffers a loss of several pixel sites at each butt joint (typically two or more from each adjacent CCD at each joint). This inherent loss of pixel sites at the butt joints results from the inability to perfectly align and finish the ends of CCD semiconductor chips.
In optical imaging applications, a loss of four pixels for every 2048 pixel sites is well within the tolerable limits, resulting only in minor streaking which can be eliminated by well-known signal processing techniques. It is therefore not an insurmountable problem in such applications.
As a result of the extremely high resolution and data rates that are obtainable with the use of CCDs, these devices have become particularly desirable in data processing applications. These applications, however, demand much higher accuracy and reliability and usually have error factor tolerances of less than 10.sup.-6. This limitation has prevented the use of CCDs in data processing applications requiring more than 2,048 pixel sites in a single array because of the inherent unreliability that occurs at the junctions of a hybrid CCD substrate. In other words, since most data playback applications call for a probability of error on the order of 10.sup.-6 or better, a loss of two or more pixels per thousand pixels cannot be tolerated.